Conventional X-ray imaging devices used to understand states of patients in hospitals have various problems in development and storage of X-ray films on which the states of patients are recorded. In order to solve these problems, digital X-ray imaging devices having a digital image detector mounted thereon have been used more and more.
In general, in a digital image detector, X-rays emitted from an X-ray source pass through an object and is then input to a fluorescent screen. The X-rays input to the fluorescent screen are converted into visible rays and are output from the fluorescent screen.
The output visible rays are reflected by a reflector and are input to a CCD camera. The CCD camera has a CCD (Charge-Coupled Device) which is an imaging device that receives visible rays and converts an image of the visible rays into electrical signals. Therefore, the visible rays input to the CCD camera are focused and are converted into electrical signals.
In such a digital image detector, since sufficient visible rays are not output from the fluorescent screen to which the X-rays are input, the distance from the fluorescent screen to the CCD camera should be minimized. However, the smaller the distance between the fluorescent screen and the CCD camera becomes, the shorter an optical path becomes and the larger an angle at which the fluorescent screen is viewed from the CCD camera, that is, a viewing angle, becomes. When the viewing angle increases, aberrations of an optical system increases in proportion to the viewing angle and it is thus not possible to obtain an excellent image.